FIELD OF THE INVENTION
The invention relates to a wafer marking which is used in the manufacture of semiconductors. A wafer or an entire batch of wafers can be identified from the marking or inscription. The coding contained in the inscription provides information about the various manufacturing and product data items, so that identification and assignment are possible at any time.
Various types of process steps are carried out on a wafer during the processing in order to produce semiconductor components, in which surface layers are removed both from the underneath and from the top. If, for example, bar codings are applied as markings, for example by a laser on the surface of a wafer, then the laser produces small depressions, points or so-called dots which produce bar codings, for example disposed in a row. These can be read by special readers for bar codings. However, the markings are subjected to all the process steps during manufacture.
Owing to the increasing number of processes and the use of so-called chemical mechanical processes (CMP), for example chemical and mechanical polishing on the front of the wafer, any inscription/marking applied to the front of the wafer is increasingly affected by the application and removal of layers. In the end, this can lead to the inscription being completely erased.
Previous markings or inscriptions on wafers are, for example, so-called hard marks, which are made very deeply on the rear of the wafer. However, such inscriptions are completely destroyed after the rear has been polished. Further disadvantages of hard marks are that the laser inscription process injects so much energy into the wafer that spattering occurs on the wafer surface. In the laser inscription process, the silicon is not melted, but it vaporizes at the processing point or at the laser impact point. As a rule, hard marks are burnt very deeply into the material. Such a depression (dot) is between 5 .mu.m and 100 .mu.m deep. Owing to the relatively large amount of energy injected, such dots are also irregular, and in some cases have sharp edges or peaks.
In addition to hard marks, it is known for so-called soft marks to be used for the marking of wafers. This can be done using the latest laser technology. The laser light is in this case injected into the wafer such that only the material at the surface is essentially melted. The inscription contains a plurality of dots produced by the laser. The result is a homogeneous inscription, free of any dirt. The depth of a normal soft mark is generally between 0.5 .mu.m and 1 .mu.m.